1. Field of the Invention
The present invention relates to plasma processors, and more particularly to a plasma processor which is well suited to turn a gas under vacuum into a plasma under the action of an electric field and a magnetic field and to process a sample such as semiconductor device substrate (hereinbelow, simply termed `wafer`) by means of ions or active species in the plasma.
2. Description of the Prior Art
A plasma processor, which turns a gas under vacuum into a plasma owing to the glow discharge and processes a sample owing to ions or active species in the plasma, has been used in various fields for ameliorating and working material surfaces and also for depositing a substance on a material surface.
It has been known that, when a magnetic field is exerted on the glow discharge based on an electric field, an electrical Coulomb force and an electromagnetic Lorentz force act. Especially with a construction wherein the electric field and the magnetic field intersect orthogonally, charged particles perform cycloidal motions, so that the frequency of collisions between particles or molecules increases to raise the density of ions or active species. With the aim of enhancing the processing rate, plasma processors applying this technique have also been proposed.
Plasma processors which employ both an electric field and a magnetic field are especially effective when applied to a sputtering apparatus, a dry etching apparatus and a vapor deposition apparatus which process substrates of silicon semiconductors and compound semiconductors. Among such plasma processors employing both the electric field and the magnetic field, an example applied to the sputtering apparatus is described in the official gazette of Japanese Patent Application Publication No. 54-32638, and an example applied to the dry etching apparatus is described in the official gazette of Japanese Patent Application Laying-open No. 58-16078.
By way of example, in the plasma processor described in the official gazette of Japanese Patent Application Laying-open No. 58-16078, a magnet element constructed of N- and S-poles is arranged under a lower electrode for placing a wafer thereon, so as to be capable of rectilinear reciprocations. In this plasma processor, a plasma based on an electromagnetic field is intensified between the N-pole and the S-pole, and the etching rate of that area of the surface to-be-processed of the wafer which has been exposed to the intensified plasma becomes particularly high. In this case, for the purpose of uniformly etching the surface to-be-processed of the wafer, the magnet element is rectilinearly scanned by a drive system so as to move the intense plasma region relative to the surface to-be-processed of the wafer. In this manner, with the plasma processor, the achievement of the uniform etching requires to rectilinearly move the magnet element from a position corresponding to one end of the surface to-be-processed of the wafer, to a position corresponding to the other end of the same. The space of the plasma processor under the electrode must be large enough to correspond to the size of the magnet element and the movement distance thereof. This leads to the drawbacks that the plasma processor inevitably becomes large in size and that the occupation area of a floor for installing the processor increases.